In the world of internet, trillions of bits of information and data are produced in every fraction of second. Thus transferring of the data over the internet needs to be protected from the intruders. Digital watermarking technique has emerged as an innovative technology to protect the data from imposters. This paper focuses different types of transform based approaches and optimization techniques used in digital watermarking. The paper reviews detailed study of particle swarm optimization and proposed methods by taking advantage of combining PSO with different watermarking schemes. The Robustness of the digital watermark implies how effective water marked image against various noise attacks. Thus it has been taken as important parameter for testing the robustness and this can be verified by evaluating NCC (Normalized Cross Correlation value) and PSNR (Peak Signal to Noise Ratio)